Since the advent of the information age, there has been a need for an efficient, fast, high capacity, and yet low cost system for the storage and retrieval of information. Ideally, such a system could be used by computers to store and retrieve digital data, document images, video images, sound recordings etc. In the past, magnetic recording devices such as floppy disk drives, hard disk drives, magnetic tape systems, etc., were used for the archival storage of information on computer systems and the like. However, magnetic recording technology is approaching physical limitations, whereas the demand for data storage and retrieval capability is increasing. This demand is expected to escalate in the future as multimedia, networking, and telecommunication applications become more sophisticated and prevalent.
One emerging technology being applied to the storage and retrieval field is that of optics. Rather than using conventional electrical signals, optical based systems utilize light beams (e.g., lasers) to convey and process information. Light beams offer advantages over electrical signals because of their high bandwidth and propagation speed. A well-known example of an optical storage system is an optical disk drive. In an optical disk drive, data is represented as a series of digital bits. A lens assembly is used to focus a light beam onto a rotating circular optical disk for reading and writing these bits to/from the disk.
Recently, flexible optical tape drives have entered the market. Optical tape drives allow for storage of digital information on a flexible optical tape with virtually limitless capacity and random access capability in a fast, efficient, and relatively cost effective manner. FIG. 1 shows a typical prior art optical tape drive system. The light generated from a light source 101, such as a laser diode, is collimated by collimator 102 to form a collimated light beam 111. The collimated light beam 111 then passes through a first relay lens 103 and focused onto modulator 104. Modulator 104 modulates the light beam. The modulated light beam is then sent through a second relay lens 105. A polarizing beamsplitter 106 is used to sample the modulated light beam. Only when the beam is modulated to a particular polarity is it passed on to the objective lens 108, which focuses the beam onto media 109. In this manner, the beam can be modulated to produce a digital bit stream representative of the information to be stored. In a read operation, the light beam, as modulated and reflected back by medium 109, is directed to a detector 110 by beam splitter 106. Detector 110 converts the received optical beam into electrical signals for processing.
In optical tape systems, the requirement to track the tape's surface while maintaining optical focus and simultaneously following a data track along the media, is normally achieved by means of a dual servo system. This dual servo system physically moves the objective lens in two axes. Very high data rate systems employing fast tape speeds imply great tape dynamics. Thus, there is a need in the prior art for a focus and track following mechanism having a high bandwidth.